Dry kiln



July 2, 1946. R. A. SIMMONS DRY KILN Filed July 1, 1944 2 Sheets-Sheet 1 INVENTOR RA SIMMOAAS by ATTORNEYS R. A. SIMMONS DRY KILN July 2, 1946.

Filed July 1, 1.944 I v F. A.

l b g g a 3 5 M M AT TO RN E'YS 2 Sheets-Sheet 2 I'NVENTOR 5/MMON6 Patented July 2, 1946 UNITED. STATES PATENT OFFICE DRYKILN R. A. Simmons, Vernonia. Oreg.

Application July 1, 1944. Serial No. 543,158

3 Claims. 1

This invention relates to dry kilns. particularly to lumber kilns, and, more specifically, to a reversible-flow dry kiln such as that described in my, U. S. Patent No. 1,636,490, dated July 19. 1927, and entitled Reversible flow dry kiln."

The present invention involves certain modifications and improvements in the dry kiln of my earlier patent, but also, as in the case of my previous kiln, has, as one of its chief objects, the providing of a lumber kiln in which the necessity of any forced air draft is entirely dispensed with.

In the kiln of my previous patent the drying currents of air are required to pass in a vertical direction up or down through the lumber, and consequently the pieces of lumber to be dried have to be separately placed on their sides and arranged in separate vertical rows to permit circulation of the drying currents of air.

Since lumber is ordinarily stacked in horizontal layers, the arrangement in spaced vertical rows requires extra. time and labor in preparing the lumber for drying in my former kiln.

One of the objects of my present invention is to provide a reversible-flow dry kiln in which the drying currents of air will be made to pass cross ways between rows of lumber stacked in the usual manner, thus enabling the lumber to be moved into the kiln and dried without extra handling.

Another object of my invention is to provide simplified and improved means for maintaining predetermined conditions throughout the kiln.

These and further incidental objects I am able to attain by constructing my improved kiln and operating the same in the manner hereinafter briefly described, in which description reference is made to the accompanying drawings. In the drawings:

Fig. 1 is a fore-shortened plan section through my improved kiln, with lumber and lumber carriers omitted:

Fig. 2 is a vertical section, more or less diagrammatic, illustrating the operation of my improved kiln when the drying currents of air are passing horizontally between the layers of lumber in one direction; and

Fig. 3 is a similar vertical section, drawn to a smaller scale, illustrating the operation when the drying currents are caused to pass in the reverse direction.

The kiln, which is rectangular in shape, and which may be' of any desired length, has the usual side and end walls In and a flat roof ll. Beams or stringers l2, extending transversely between the side walls, and located a substantial distance above the ground, support the central flooring l3 and the parallel rails I4 on which the lumber cars or conveyors I! run. The flooring l3 extends the full length of the kiln, but does not extend to the sides of the kiln, the reason for which will become apparent later. A pair of baiiie walls l6 and I6, extending the entire length of the kiln, are located at the side edges of the flooring l3 and slope obliquely downwardly, as shown in Fig. 2. their lower edges being located a short distance above the ground and their upper edges extending slightly above the surface of the flooring.

At spaced intervals in the side walls upwardlyextending air outlets or vents I! are located. The entrances to these air outlets are close to the ground or bottom of the kiln, as shown in Fig. 2, and these outlets preferably terminate in stacks l8 extending above the roof in order to promote. the drawing of air from the bottom of the kiln up through these outlets I! for discharging to the outside atmosphere.

Heating coils i9 and [9, supported by the and 21 control the passage of steam through the pipe sections 22 and 23 respectively.

The endwalls of the kiln are provided with suitable doors (not shown) so that cars l5 conveying the lumber can be run into the kiln from one end. and, after the desired treating of the lumber is completed, can be moved out of the kiln from the other end. The kiln, of course. can be made long enough to accommodate several such cars of lumber, and all the cars may be moved into and out of the kiln together or they may be delivered into the kiln one at a time and similarly removed one at a time from. the opposite end, thereby allowing each car load the full time desired for the treatment in the kiln.

During the kiln-drying of the lumber air enters the kiln through either of the two conduits .28

and 28f located at opposite sides near the bottom of the kiln and extending the full length'of, the kiln. Both ends of each of these conduits extend beyond the outside end walls, as shown in Fig. .1; 1

Hinged doors 2!! at each end of conduit 26 and atoms; I

similar hinged doors 28' at each end of conduit 28' control the passage of outside air into these conduits. Suitable manual-means (not shown) for keeping the hinged doors 28 and 28' opened or closed, as desired, are provided.

The top wall of each of the conduit 28 and 28' is provided with a series of identical transverse discharge slots 38. These slots are equally spaced throughout the length of the conduits to permit air entering into either conduit to be distributed throughout the whole length of the kiln. In order to insure equal distribution of such air through the kiln I have found that it is necessary to restrict the area of the slots, otherwise there will not be suflicient air entering into the conduit to insure the discharge of air from the slots located near the center of the conduit. If the total area of these top discharging slots is kept to about 75% of the combined area of the two doors at the ends of the conduit, for example, a very satisfactory and 'even distribution of incoming air throughout the entire length of the kiln will be maintained. Thisis an important feature in .ny kiln, namely, that an even distribution and ;irculation of air will occur constantly throughout the kiln regardless of its length and without requiring any forced draft.

In order to prevent the air entering into the kiln from becoming too dry, and thus causing too rapid withdrawal of the moisture from the lumber, which would have an injurious effect on the lumber such as causing checking, etc., I provide perforated steam pipes 3| and' 3| extending longitudinally above the conduits 28 and 28' respectively. The perforations in these pipes are arranged so as to cause jets of steam to be emitted vertically, thus causing the steam vapor to mix with the currents of air pressing upwardly from the discharge slots 30 of the conduit 28 or of the conduit 28 as the case may be. These perforated steam pipes are connected to the main steam line 2| by the pipe sections 22 and 32 and the branch pipes 33 and 83', as shown in Figure 1. A valve 35 controls the passage of steam into the pipe section 32, and valves 34 and 34' control the passage of steam through the branch pipes 33 and 33' respectively.

The operation of my improved kiln is as follows:

When the lumber to be dried has been placed in the kiln and the kiln is closed, one of the conduits, for example conduit 28, is opened, the doors 29 of the other conduit 28' being kept closed. The valves 26, 21 and 25 are opened and valve 25' is kept closed. This causes steam to pass into the heating coils I9. Likewise valves 35 and 34 are opened, while valve, 34' is kept closed. This causes steamto pass into the perforated pipe 8|. Air from the outside entersthe conduit 28 and passes upward into the kiln through the discharge slots 30 in the top ofthe conduit 28. Sincethe area of these slots is restricted and their combined area is less thanthe cross-sectional area of the doors 29, the incoming air will be delivered through these slots throughout the entire length of the kiln. As the incoming cool air passes upwardly through these slots steam vaporfrom the pipe 8| mixe with the air to cause some humidity in the air and thus prevent the incoming air from being toodry when it is heated and applied to the lumber. The incoming air rises past the heating coils l8 which increase its temperature to the desired temperature for kiln-drying the lumber. The flooring is omitted between the baflle wall l8 and the adjacent wall of the kiln in order to permit this free passage of air upwardly past the heating coils IS. The direction of the heated currents of air is now indicated by the arrows in Fig. 2. Since the air in the kiln is warmer than the outside air there will be an upward draft through the outlets or vents l1, and particularly through those which are located on the opposite side of the kiln from that on which the conduit 28 is located. The currents. of air are thus drawn through the lumber in the channels between the horizontal layer in which the lumber is stacked.

In order that the lumber on both sides of the stack will be subjected to the same treatment, that is, to prevent the lumber on one side drying faster than that on the other side, the direction of the drying currents of air is reversed at the half stage. Toaccomplish this reversal the doors 29' of the conduit 28' are opened and the doors 29 of the conduit 28 are closed. Valve 25 is opened and valve 25 is closed, causing the coils l9 now to be heated. Similarly valve 34' is opened and valve 34 is closed causing steam to pass into the perforated pipe 3|. The currents of air will now pass in the direction indicated by the arrows in Fig. 3, thus resulting in the lumber at both sides of the stack receiving equal treatment, and, due to the equal distribution of the incoming heated currents of air throughout the entire length of the kiln this equal treatment occurs throughout the entire length of the stack or stacks of lumber in the kiln.

It is very desirable that the proper conditions of temperature and humidity be maintained constantly during the kiln-drying of the lumber so that the best results will be assured. While this can be done by having an operator check the temperature and humidity from time to time, it is more practical, and permits a saving in op- .erating costs, to have this control take place automatically. For this purpose I use a dual automatic controller indicated diagramatically at 36 in Fig. 1, this controller being of the type frequently used for similar purposes, and electrically connect the controller to electric means associated with the valves 21 and 35. This automatic controller includes means 31, commonly known as bulbs, which are effected respectively by heat and humidity conditions. This means 31 is located within the kiln and preferably at some central point as indicated in Figs. 2 and 8. The operation of the automatic control is very simple.

v Should the temperature within the kiln at any time rise above the amount for which the control is set, this will cause the valve 21 automatically to be closed. This temporarily shuts off the steam to the heating coils until the temperature drops below the desired maximum, whereupon the valve 21 will again be automatically opened. Similarly when the humidity within the kiln rises above the 4 desired amount the valve 35 will be automatically closed thus temporarily shutting off the steam to the perforated pipe 3| or 3|, as the case may be, causing the incoming air to be drier and thus lowering the relative amount of humidity in the kiln until the humidity drops enough to cause the valve 35 to be automatically opened. While I have referred to the automatic'control as electrically connected and having electric valve-operating means, similar automatic controls for heat and humidity are alsoobtainable which are oprated by compressed air. Either type may conveniently be used with my kiln.

. Thus when the lumber is placed in the kiln and the conditions of temperature and humidity a v awai s a and the length of time required -for the kiln- I drying of the particular grade of lumber are establish'ed, the only operation necessary is the reversal of the air currents when half of the prescribed period for the kiln-drying has elapsed. This reversal of the air currents, as previously explained, is done very quickly and easily. Since no forced draft is used in the kiln and nothing else is required for the operation oi. the kiln-drying process other than a constant steam supply, my kiln can be operated at a minimum of expense and labor and with the certainty of accurate results. After the completion oi the kiln-drying process the lumber carriers are moved out of the kiln and since the lumber is stacked in the usual manner for transportation a minimum handling of the lumber is necessitated.

I claim:

1. A dry kiln of the character described including air outlets located at the sides of the kiln, the. entrances into said outlets located near the bottom of the kiln, a pair of air conduits extending longitudinally through the kiln. said conduits located at the sides of the kiln respectively and immediately above the entrances into said outlets, means at the ends of said conduits con trolling the passage of outside air into said conduits, slots in the top walls of said conduits, the total area of the slots of each conduit being less than the cross-sectional area at the entrances to the conduit, a spray pipe located above each conduit, heating, coils located above each conduit and spray pipe, whereby the air entering into the kiln through either conduit can be humidified and heated as it passes upward from said slots, a cen- 01' the conduit, a perforated steam pipe located above each conduit, heating coils located above each conduit and perforated steam pipe, whereby the air entering into the kiln through either conduit can be humidified and heated as it passes upward from said slots, 9, central flooring ext-ending the length of the kiln, said flooring spaced from the sides of the kiln and located above said conduits, baiiie walls extending downwardly from each side of said flooring, the conduits andcoils located between the baflle walls and the side walls of the kiln respectively, the bottom edges of said bailie walls located below the tops of said conduits and spaced from said conduits respectively, said baille walls preventing currents oi. air from passing crosswise immediately below said flooring and said flooring preventing currents of air from moving in vertical direction a: the longitudinal center of the kiln, whereby the opening of one or said conduits and the closing of the other of said conduits will cause air currents to pass more. or less in horizontal direction from one side of the kiln to the other above said flooring, and the opening of said other conduit and the closing of the first mentioned conduit will cause air currents to pass in reverse horizontal direction above said flooring, conveyor-supporting means extending along said flooring, a system of valves controlling the passage of. steam into said perforated steam pipes and heating coils to enable delivery of steam to be restricted to the heattral flooring extending the length of the kiln,

said flooring spaced from the sides of the kiln and located above said conduits, baflie walls extending downwardly from each side of said flooring, the conduits and coils located between the baflle walls and the side walls of the kiln respectively, the bottom edges of said baiile walls spaced from said conduits respectively, said baiile walls preventing currents of air from passing crosswise immediately below said flooring and said flooring preventing'currents of air from moving in vertical direction at the longitudinal center of the kiln, whereby the opening of one of said conduits and the closing of the other of said conduits will cause air currents to pass more or less in horizontal direction from one side of the kiln to the other above said flooring, and the opening of said other conduit and the closing of the first mentioned conduit will cause air currents to pass in reverse horizontal direction above said flooring, conveyor-supporting means extending along said flooring, and a system of valves controlling the passage of steam into said spray pipes and heating coils to enable delivery oi'steam to be restricted to the heating coils and spray pipe located above the conduit which is open.

2. A dry kiln comprising air outlets spaced at equal distances along the sides of the kiln, the entrances into said outlets located near the bottom of the kiln, a pair of air conduits extending longitudinally through the kiln, said conduits located at the sides of the kiln respectively and immediately above the entrances into said outlets, a hinged door at each end of each conduit controlling the entrance of air into the conduit,

slots in the top walls of said conduits, said slots spaced at equal distances along said conduits, the total area of the slots of each conduit being less than the combined area of the doors at the ends air ,into the conduit,

ing coils and perforated steam pipe located above the conduit which is open, and an automatic mechanism associated with said system of valves,

humidity and temperature controls included in said automatic mechanism, whereby the heat and humidity within'the kiln will be prevented from rising above predetermined limits.

3. A dry kiln comprising air outlets spaced at equal distances along the sides of the kiln, the entrances into said outlets located near the bottom of the kiln, said outlets terminating in stacks extending above the top of said kiln, a pair of air conduits extending longitudinally through the kiln, said conduits located at the sides of the kiln respectively and immediately above the entrances into said outlets, a hinged door at each end of each conduit controlling the entrance of transverse slots in the top walls of said conduits, said slots spaced at equal distances along said conduits, the total area 01' the slots of each conduit beingnot more than 75% of the combined area of the doorsat the ends of the conduit, a spray pipe located above each conduit, heating coils located above each conduit and spray pipe, whereby air entering into the kiln through either conduit can be humidified and heated as it passes upward from said slots, a central flooring extending the length of the kiln, said flooring spaced from the sides of the kiln and located above said conduits, bafile walls extending obliquely downwardly from each side of said flooring, the conduits and coils located between the baiiie walls and the side walls of the kiln respectively, the bottom edges of said baiile walls located below the tops of said conduits and spaced from said conduits respectively, said baiile walls preventing currents of air from passing crosswise immediately below said flooring and said flooring preventing currents of air from moving in vertical direction at the longitudinal center of the kiln, whereby the opening of one of said conduits and the closing of the other of said conduits will cause air currents to P ss more or less in horizontal direction from one side '01 the kiln to the other above said floor?- ing, and the opening of said other conduit and the closing of the first mentioned conduit will cause air currents to pass in' reverse horizontal direction above said flooring, conveyor-supportmg means extending along said flooring, a system of valves controlling the passage of steam into said spray pipes and heating coils to enable delivery of steam to be restricted to the heating coils and spray pipe located above the conduit 1 8 which-is open, and an automatic heat and humidity control forv the kiln, said automatic control including electrically operated mechanism associated'with said valve system and heat and humidity bulbs located within said kiln and connected with said electrically operated mechanism, whereby the heat and humidity within the kiln will be prevented from rising above predetermined limits. v

R. A. SIMMONS. 

